Advanced circulatory system physiology | Health and medicine | Khan Academy
A high systolic blood pressure generally means there is a greater resistance that the heart has to work against during Relationship Among Vascular Area, Blood Flow Velocity and Blood Pressure ▻Try the Cardiovascular Physiology quiz!. View the animation below, then complete the quiz to test your knowledge of the concept 5, Blood flow is affected by both blood pressure and vessel resistance. This learning tool, which includes the quiz and worksheet, can be. of an artery's lumen increases pressure; Poiseuille's Law in relation to blood flow regulation.
This can cause red cells to stick together and form chains of several cells rouleau formation within the microcirculation, which increases the blood viscosity. Because of the high degree of interaction between the elements of blood when it is not flowing, a driving pressure significantly greater than zero is required for stationary blood to start flowing again.
Although plasma is mostly water, it also contains other molecules such as electrolytes, proteins especially albumin and fibrinogenand other macromolecules.
Pressure and Blood Flow
Because of molecular interactions between these different components of plasma, it is not surprising that plasma has a higher viscosity than water. The addition of formed elements to plasma red cells, white cells, and platelets further increases the viscosity.
Of these formed elements, red cells have the greatest effect on viscosity. Therefore, blood viscosity strongly depends on hematocrit. Increased viscosity increases the resistance to blood flow and thereby increases the work of the heart and impairs organ perfusion. Some patients with anemia have low hematocrits, and therefore reduced blood viscosities.
Another important factor that influences blood viscosity is temperature. Just like molasses, when blood gets cold, it becomes "thicker" and flows more slowly.
Therefore, there is an inverse relationship between temperature and viscosity. Normally, blood temperature does not change much in the body.
Advanced circulatory system physiology
However, if a person's hand is exposed to a cold environment and the fingers become cold, the blood temperature in the fingers falls and viscosity increases, which together with sympathetic-mediated vasoconstriction decreases blood flow in the cooled region.
When whole body hypothermia is induced in critical care or surgical situations, this leads to an increase in blood viscosity and impaired organ blood flow. There are 3 factors that determine the resistance to blood flow: Vessel radius is the most powerful regulator of the blood flow, since it is raised to the 4th power.
Therefore if the vessel radius is reduced by half, flow is decreased by a factor of Relationship Among Vascular Area, Blood Flow Velocity and Blood Pressure Large blood vessels have faster rates of blood flow and higher pressure, but small total areas. On the other hand, capillaries have a large total area, slow rate of flow and low pressure.
Hemodynamics (Pressure, Flow, and Resistance)
This allows time for nutrient exchange between the capillaries and tissue. The relationships among total vessel cross-sectional area top panelvelocity of blood flow middle panel and blood pressure in the vessel lower panel.
The large arteries have smaller areas and higher velocity and pressure, while the capillaries have a larger total area, and low velocity and flow rates to enhance the time and area for nutrient exchange to occur.
The major control mechanisms of vessel radius are: Sympathetic nerve fibers innervate the smooth muscles of small arteries, arterioles and precapillary sphincters. Sympathetic fibers that supply the vessels of organ beds release of norepinephrine noradrenalin and cause vasoconstriction.